This invention relates to methods for dressing grinding wheels and, more particularly, relates to dressing methods using abrasive compacts.
As set forth in Oberg et al., Machinery's Handbook, p. 1991 (20th Ed., 1976): "The perfect grinding wheel operation under ideal conditions will be self sharpening; i.e., as the abrasive grains become dull, they will tend to fracture and be dislodged from the wheel by the grinding forces, thereby exposing, new, sharp abrasive grains. While in precision machine grinding this ideal may be partially attained in some instances, it is almost never attained completely. Usually, the grinding wheel must be dressed and trued after mounting on the precision grinding machine spindle and periodically thereafter. PA1 Dressing may be defined as any operation performed on the face of a grinding wheel that improves its cutting action. Trueing is a dressing operation but is more precise, i.e., the face of the wheel may be made parallel to the spindle or made into a radius or special shape. Regularly applied trueing is also needed for the accurate size control of the work, particularly in automatic grinding."
Opening is another dressing operation and refers to the breaking away of the bond material from around the abrasive particles in a wheel thereby exposing them for grinding. A new wheel is initially opened and may have to be periodically opened thereafter to expose new particles when the previously exposed particles have been dislodged or dulled and to remove grinding swarf, which may accumulate during grinding, from around the abrasive particles.
A cluster compact is defined as a cluster of abrasive particles bonded together either (1) in a self-bonded relationship, (2) a means of bonding medium disposed between the crystals, (3) by means of some combination of (1) and (2). Reference can be made to U.S. Pat. Nos. 3,136,615; 3,141,746 and 3,233,988 for a detailed disclosure of certain types of compacts and methods for making same. (The disclosure of these patents are hereby incorporated by reference herein.)
A composite compact is defined as a cluster compact bonded to a substrate material such as cemented tungsten carbide. A bond to the substrate can be formed either during or subsequent to the formation of the cluster compact. Reference can be made to U.S. Pat. Nos. 3,745,623; 3,743,489 and 3,767,371 for a detailed disclosure of certain types of composite compacts and methods for making same. (The disclosure of these patents are hereby incorporated by reference herein.)
A table of a dressing tool is the tool surface against which chips of the grinding wheel bear as they are being severed.
Rake angle refers to the angle of engagement of a dressing tool with a wheel as measured from the tool table as a plane of reference. Back rake angle is defined herein as the angle measured in a plane perpendicular to the wheel spindle which is formed between the table of the tool and a line originating at the center axis of the wheel and extending radially outward through the line or point of intersection of the wheel surface and said table of the tool tip. Back rake angles are considered to be positive when measured in the direction of wheel rotation from the extension of the radius to the tool table. That is, by reference to FIG. 2 herein, the angle is negative and positive when the extension of the radius is "below" and "above" the tool table, respectively.
Side rake angle is defined herein as the angle measured in a plane parallel to the wheel spindle which is formed between a table of the tool tip and a line parallel to the wheel spindle. Side rake angles are considered to be positive when measured from a line parallel to the table in a clockwise direction-assuming a left to right tool feed and a clockwise wheel rotation.
Side cutting edge angle is defined as the angle between the leading side of tool (i.e., the right side assuming left to right tool feed) and a plane parallel to the axis of the tool shank.
End cutting edge angle is defined as the angle between the trailing edge of the tool (i.e., the left side of the tool assuming left to right tool feed) and a plane perpendicular to the axis of the tool shank.
Reference can be made to the aforementioned Machinery's Handbook, pp. 1992 to 1994 for a listing of commonly used dressing tools and methods for their use. One common type is a single point diamond tool having a granular shaped diamond mounted at one end of a tool shank. (See FIGS. 1, 1A herein.) Dressing is performed with such a tool by engaging the periphery of a rotating wheel with the cylindrical handle of the tool disposed at an angle of 10.degree. to 15.degree. relative to a line drawn perpendicular to a tangent to the wheel periphery at the point of engagement of the tool with the wheel. This is equivalent to a negative back rake angle of about 55.degree. to 60.degree.. (The back rake angle of a single point diamond tool is not easily defined and measured in terms of a face of the diamond tip because of the irregular shape of the tip which varies from one tip to another.) The tool is also occasionally rotated about its longitudinal axis to prolong diamond life by limiting the extent of the wear facets and also to produce a pyramidal shape of the diamond tip.
It is also known to shear the natural diamond tip to reduce the negative back rake angle. Even with the shearing, these tools are used at a negative back rake angle. It is also known to use such tools with the longitudinal axis of the handle at a 0.degree. angle relative to a line perpendicular to the tangent to the wheel periphery at the point of engagement of the tool with the wheel. However, the tip is still at a negative rake angle. (see FIG. 1A herein.)
Another dressing tool which has been recently developed is a tool comprised of a cylindrical tool shank with a composite diamond compact tip fixed at one end. The diamond and carbide layers are oriented parallel to the longitudinal axis of the tool shank. Such composite compacts have been used to dress a grinding wheel by engaging the periphery of the wheel to an exposed edge of the compact with the edge transverse to the diamond layer. The tool is disposed (i) at either a zero degree back rake angle or a negative back rake angle and (ii) at a zero degree side rake angle.
While the prior methods for dressing are generally considered to be satisfactory, manufacturers are always concerned with improving the grinding process, such as by improving wheel life, surface finish on the workpiece produced by the grinding wheel, dressing tool life and dressing speeds.
Accordingly, it is an object of this invention to provide a dressing method which enhances and improves the grinding process in these areas.
Another object of this invention is to provide an improved dressing tool particularly applicable for dressing at positive rake angles.